Optical readout devices have been coupled with any number of input sources. Such sources include direct inputs from position sensors, or indirect inputs from computational circuitry or algorithms which perform functions from one or more inputs. One example might be a digital conversion from an initial analog input or inputs.
Of particular interest are optical devices which apply an algorithm or a constant conversion factor to an initial input or inputs. For example, a linear input can be converted to diameter or circumference by application of the pi conversion factor, 3.14159 and on to as many decimal places as necessary, as is well known.
As an example, there are a myriad of uses for linear tapes which can be formed into a circle around the outside or the inside of a circular object to provide readings for circumference or diameter. A pi conversion can be incorporated into a vernier device with permanent markings on the end of the tape that cooperatively aligns with the vernier device to provide visual readings of diameter. Of course, length (circumference) markings can be read directly with the tape in place on or in the object being measured. An example is shown in PI TAPE Precision Periphery Tapes Direct Diameter Reading (January 1991).
It is well known that vernier readings, however precise, are still approximations at the very point of precision. Not only is there some element of interpolation, the number or distance read depends on the eyesight and care of the user, and possibly on the amount of tension applied to the two elements of the vernier device.
It is known that digital tape measures where a conversion element may be either capacitive, magnetic, or photoelectric, is used to determine the amount of movement or position of a tape and generate a signal corresponding to that amount of movement of the tape, exist in the marketplace today. There are many different digital devices used with tapes that produce this effect for linear measurement applications as demonstrated by U.S. Pat. Nos. 4,611,402 and 8,356,419. It is also known that non-electronic, non-digital insertion tape techniques can be used to make circumference and diameter measurements with a simple window reading, or a vernier reading, also visually in a window arrangement, as demonstrated by Zerfis, Am. J. Clin. Nutr. 28; 782-787 (1975).
As suggested above, in all measurement tapes there exists the problem of reading or interpreting the hash marks on the tape to get the final measurement. In linear tapes this can be very difficult and can lead to measurement errors. In insertion tapes for radial measurements this problem is an order of magnitude larger where multiple marks must be read with an understanding of the relationship between the hash marks for the user to calculate the final measurement.
Digital tape readers solve the problem of reading hash marks to convert measurements to a known value. To date there have been many that do this for linear applications.